Rollback support in ForestDB

The rollback API allows the applications to rollback their database to a specific point that is represented as a sequence number.

Here is the rollback API definition:

LIBFDB_API
fdb_status fdb_rollback(fdb_handle *handle, fdb_seqnum_t seqnum);

This API does a reverse scan on the given database handle until it finds the database header whose last sequence number <= seqnum, and then rollbacks the database to that header state, and returns FDB_RESULT_SUCCESS. If it can't find the header, then it will return FDB_RESULT_ROLLBACK_FAIL.